In the field of optical communication networks, the expression “Fiber-to-the-x” (“FTTx”) is used to denote a network architecture making use of optical fibers. In particular, the expression “Fiber-To-The-Premises” (“FTTP”) denotes the portion of the optical communication network that reaches the premises (home, offices and the like) of the end customer. The expression “Fiber-To-The-Home” (“FTTH”) denotes the portion of the optical communication network that reaches the home of the end customer.
A FTTH network is an optical communication network providing a number of end customers with broadband communication services, i.e. with services requiring data transmission at a rate of more than a few Mbit/s.
Typically, a FTTH network comprises a distribution cabinet cooperating with a transport network, a plurality of termination boxes and a plurality of optical fibers. Each termination box is connected to the distribution cabinet by means of one or more optical fibers.
Typically, a distribution cabinet is located in the basement of a building, in which building the end customers reside, whereas termination boxes are arranged at the various building floors, within or in proximity of the apartments and/or offices of the end customers.
An optical cable comprising a plurality of optical fibers typically exits the distribution cabinet. In the following of the present description, an optical cable which exits a distribution cabinet and serves each floor of a given building to reach each end customer will be indicated as “in-line optical cable” or “riser cable”.
FTTH installations are largely characterized by the presence of multi-dwelling units (MDUs). Such units may comprise up to several tens of potential customers who are concentrated onto a relatively small area and are typically distributed in a vertical dimension.
Therefore, typically, the in-line optical cable runs through the building from the basement up to all the building floors. The in-line optical cable is typically laid down within a conduit, which protects the in-line optical cable.
In new buildings such conduits are generally empty and fully available for the passage of such rising cables. On the contrary, in existing buildings the conduits are generally at least partially occupied and it may be difficult to perform installation. In any case, the riser cable may be typically subject to bends when it is installed in both new and existing conduits.
Typically, an optical cable, which comprises one or more optical fibers, exits each termination box installed at an end customer's apartment/office of the building. An optical cable which exits a termination box is typically indicated as “drop cable”.
Connecting the distribution cabinet to a termination box requires extracting at least one in-line optical fiber from the in-line optical cable and connecting such an in-line optical fiber to a drop optical fiber of said drop cable exiting the termination box. The optical connection between the in-line optical cable and the drop cable is typically made in a so-called “optical transition box”.
The Applicant has faced the problem of providing an optical cable, in particular an optical riser cable, which has a relatively reduced outer diameter while has a high fiber count and which can be more easily bent in order to install it in conduits, either existing conduits or new conduits. It should be remarked that providing an optical cable having a relatively reduced outer diameter and a high number of optical fibers are conflicting requirements.
The Applicant has also faced the problem of providing such a riser optical cable having an optical fiber modularity, namely a fiber optical cable wherein all the optical fibers are arranged into several groups, with each group of optical fibers comprising one or more optical fibers. Typically, each group of optical fibers comprises the same number of optical fibers. Each group of optical fibers could be advantageously dedicated to a single customer. Indeed, providing a plurality of optical fibers to a single customer is becoming a requirement of national telecom authorities which want to offer more competition among telecommunication providers. This because each single optical fiber reaching the premise of a customer can be used by a different telecommunication provider. After the installation of the optical cable the only operation required to a customer in order to change provider is to switch to the appropriate fiber.
Several optical cables are known in the art.
For instance, U.S. Pat. No. 6,185,352 discloses a fiber optic fan-out cable having optical sub-units. The optical sub-units are disposed about a central member, at least some of the optical sub-units each respectively comprising a sub-unit jacket, strength fibers, and at least one respective optical fiber ribbon therein. The optical fiber ribbon including a plurality of optical fibers, the strength fibers generally surrounding and contacting the optical fiber ribbon within the sub-unit jacket. A cable jacket surrounds the central member and defines an annular space wherein the optical fiber sub-units are disposed about the central member. The annular space including essentially no strength fibers therein outside of the sub-unit jackets, the strength fibers being essentially located within the optical sub-unit jacket with the respective optical fiber ribbons. One or more layers of optical sub-units, that can be bundled with a conventional binder tape or cord, are preferably helically (unidirectionally) or SZ stranded about the central member in the annular space. Cable jacket has an outside diameter of about 8 mm to about 30 mm, as determined by the number of sub-units that are in the particular cable. The number of sub-units in a cable may vary from, for example, 3 to 36.
U.S. Pat. No. 7,536,071 discloses an optical cable for communication including at least one micromodule, wherein the micromodule is blocked with respect to the propagation of water. The at least one micromodule comprises a plurality of optical fibers, for example a bundle of optical fibers, includes at least one optical fiber, a retaining element for housing the at least one optical fiber, and a thixotropic filling compound arranged within the retaining element. The micromodule comprises a plurality of optical fibers, for example a bundle of optical fibers. The plurality of optical fibers is housed within the retaining element in a loose manner.
U.S. Pat. No. 6,067,394 discloses a modular optical transmission cable which has several reinforcement and optical modules, each optical module having: a sheathed optical fiber, coated with: an intermediate decoupling layer, and with a rigid shell forming a microcarrier, a reinforcement module being associated with an optical module, the modules being molded in an external sheath. A flexible reinforcement module is associated with at least one optical module that is self-reinforced against compression in order to obtain a cable having high flexibility combined with high compressive strength. The disclosure can be applied in the field of optical fiber cables and especially that of the reinforcement structures of such cables and fibers.
No one of the cables disclosed in the above cited prior art provides the desirable requirements in terms of reduced diameter, high fiber counts, optical fiber modularity and high capability to be bent for being installed in conduits, either existing conduits or new conduits.
All requirements are particularly desirable when the optical fiber cable is used for installing an FTTP or FTTX network.